Compound apex for vehicle tire

ABSTRACT

A pneumatic radial ply tire ( 500 ) comprises a tread ( 510 ), a belt structure ( 512 ), and a carcass ( 514 ). The carcass ( 514 ) has a radial ply ( 518 ) and two bead sections ( 530 A,  530 B). Each bead section ( 530 A,  530 B) has a bead ( 532 ) and a component apex ( 534 ) with a inner apex ( 534 A), a middle apex ( 534 B) and an outer apex ( 534 C).

TECHNICAL FIELD

The present invention relates to an improved design for a radial plyautomobile tire, and more specifically to an improved apex for a radialply automobile tire.

BACKGROUND OF THE INVENTION

A conventional radial-ply automobile tire includes radial plies that arewrapped around two annular inextensible beads. In the tire makingprocess, a green tire carcass (“green” meaning as yet uncured and stilltacky) is built by sliding a green innerliner and radial ply over a tire“building drum” (or “building mandrel”). Two beads (each comprising acable of steel filaments encased in green rubber) are then slid over thecarcass, one at each side. The portions of the plies that extend beyondthe beads are then turned up around the beads, forming “turn-ups”. Then,the portion of the plies between the beads is expanded radially outwardso as to contact the ply turn-ups. The annular cross-sectionallytriangular rubber filler bounded by the turned up ply and the bead iscalled an “apex”.

There are two methods of incorporating the apex during the tire-makingprocess. In the “pre-apexing” method, an apexing machine adheres anannular triangular apex to an annular bead. The bead, with the apexstill adhering to it, is slid over the carcass on the building drum. Theplies are then turned up and expanded as mentioned above, so that theapex is surrounded by the bead from below and by the plies from thesides.

In the “flat application of apex” method, the apex is circumferentiallylaid down onto the carcass while on the building drum. The apex is laiddown as a triangular strip of green rubber (“gum strip”) lyinghorizontally on the carcass, next to the bead, so that one of its tackylong flat sides adheres to the tacky green carcass, and its short baseis close to, and faces, the bead. When the portion of the plies betweenthe beads is expanded outward, the apex's wedge profile swings around 90degrees, and rests atop the bead, aligned vertically.

The choice of triangular dimensions and material properties of the apexaffects the performance of the tire, such as tire weight, sidewallstiffness, handling, ride comfort, flexural heat, material fatigue, andtire life. For example, since the apex extends up much of the length ofthe sidewall, increasing the stiffness of the apex increases thestiffness of the sidewall, yielding less sidewall flexing and hence lessflexural heat and material fatigue, but at the cost of a rougher ride.Increasing the apex's radial length (so that it travels farther up thesidewall) further stiffens the sidewall and improves handling, which isbeneficial for “high performance” tires.

Tire designers at Goodyear Tire and Rubber Company have found that theywould have wider choice of, and tighter control over, tire performanceif they had wider flexibility in choice of apex design—that is, if theycould specify longer apexes than conventionally used, and apexes withmultiple layers of different material (“compound apexes”).

However, in the pre-apexing method, the radial length of the apex islimited by inadequacies of splicing and by the tendency of the apexprofile to bend at its tip, called “curl-over”. Apex splices, where theends of a length of extruded rubber are spliced together to form anannular apex, are imperfect. Apex curl-over and splice imperfection areaggravated by longer radial length and softer material.

The “flat application of apex” method does not have the radial lengthlimitation experienced by the pre-apexing method, because its apex islaid horizontally against the carcass. However, it does suffer fromentrapped air which can cause internal delaminations.

The “pre-apexing” method is not suitable for making compound apexes,because the compound extrusion required for such an apex is complex toextrude and prone to deformation while standing vertical on the bead inthe soft green state. The “flat application of apex” method is notsuitable for making compound apexes because increasing the number ofapex layers increases process time and requires a more complex extruderin the building drum area.

The following patents disclose bead assemblies having either amultilayered apex, a rubber material adjacent to an apex, or a flatrubber material between the bead and ply. U.S. Pat. No. 4,319,943discloses a method of securing a bead filler material to a bead bypositioning “bead filler portions” (apex) on top of “reinforce material”(plies) on either side of the bead bundle, and folding the reinforcematerial around the bead bundle. U.S. Pat. No. 4,934,431, in FIG. 3,discloses a bead filler 6 (apex) disposed above a ring of bead wire 3(bead) and a “bead reinforcing layer 8 disposed within the foldedportion of the carcass 4 and extending about the bead wire 3” whereinthe reinforcing layer 8 may be composed of cords of carbon fiber with arubber latex adhesive. U.S. Pat. No. 4,227,563 discloses a tire in which“a first filler element 78 is provided to separate the turnup 30 fromboth the apex strip 70 and the carcass ply 28” and which also has secondand third filler elements 84, 86. U.S. Pat. No. 5,374,324 discloses anapex of triangular cross-section formed of multiple apex leafs radiallycontacting each other. U.S. Pat. No. 5,309,971 discloses a bead assemblyhaving a rubber bead filler 84 (apex) and a reinforced rubberized plyflipper 86. U.S. Pat. No. 5,221,385 discloses a tire having a bead core5 (bead), a bead filler 6 (apex), and a rubber sheet 13. U.S. Pat. No.3,163,683 discloses a tire bead assembly having a bead core, an apex anda gum tie strip of uncured rubber material. U.S. Pat. No. 4,319,943discloses a prior art bead subassembly (FIG. 1A) having bead fillerportions 30, 32 on the top surfaces of material wings (sections of ply)axially spaced from the bead bundle annular side surfaces 16,18.

JP 61 069438 discloses manufacture of a bead apex by a method wherein abead core side part and a point side part are formed individually, andboth parts are connected in a body and are made in to the bead apex. Thebead apex 5 comprises a base part 5a and an end part 5b. The base part5a is formed and attached (apparently preassembled) to the bead core.There is an end part 5b which is disposed on a carcass ply 7 on a drum11.

EP 0 826 534 discloses a pneumatic radial tire having a rubber filler 7composed of three different rubber stocks 7-1, 7-2, 7-3.

SUMMARY OF THE INVENTION

The present invention relates to a method of building a green tirecarcass by wrapping a ply having a pair of spaced preassembled innerapexes around a building drum. Then, a pair of beads with preassembledmiddle apexes are mounted circumferentially over the ply to a locationaxially outward from the inner apexes. Next, the middle section of theply between the inner apexes is expanded radially outward to bring theinner apexes against the middle apexes. Preferably, the ply has a pairof preassembled outer apexes, each outwardly spaced from one of theinner apexes. Each of the beads is positioned with the preassembledmiddle apexes between corresponding inner and outer apexes. Next, theply turnup portions of the ply are turned up to bring the outer apexesagainst the corresponding middle apexes.

Preferably, the inner apexes and the outer apexes have a rectangularcross-section, and the middle apexes have a substantially triangularcross-section. The inner apexes extend radially outward further than theouter apexes and the middle apexes extend radially outward less than theouter apexes. The inner apexes, the middle apexes and the outer apexesare selected from a material of the group consisting essentially ofgreen rubber, cured rubber, and combinations thereof.

Also according to the invention, a pneumatic radial ply tire comprises atread, a belt structure, and a carcass. The carcass has a radial ply andtwo bead sections. The tire is characterized by each bead section havinga bead and a compound apex with an inner apex and a middle apex. Thecompound apex preferably also has an outer apex. The inner apex and theouter apex have a substantially rectangular cross-section, and themiddle apex has a substantially triangular cross-section. Preferably,the inner apex extends radially outward further than the outer apex andthe middle apex extends radially outward less than the outer apex. Theinner apex, the middle apex and the outer apex are each of a materialselected from the group consisting essentially of green rubber, curedrubber and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made in detail to preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. The drawings are intended to be illustrative, not limiting.Certain elements in some of the drawings may be illustrated not-to-scalefor illustrative clarity.

In the drawings, the hundredth's place of each reference number usuallymatches the figure number, and similar elements are usually referred toby similar reference numbers. For example, element 199 in FIG. 1,element 299 in FIG. 2, and element 399 in FIG. 3 usually indicatecorresponding or substantially similar elements.

In a single drawing, similar elements may be assigned the same number.For example, both beads of the same tire may be assigned the samenumeral.

For illustrative clarity, the cross-sectional views presented herein maybe “near-sighted” cross-sectional views, omitting certain backgroundlines that would otherwise be visible in a true cross-sectional view.

The structure, operation, and advantages of the invention will becomefurther apparent upon consideration of the following description takenin conjunction with the accompanying drawings, wherein:

FIG. 1A shows a meridional cross-section of a typical conventionalradial ply pneumatic tire;

FIG. 1B shows a cross-section of the bead section of FIG. 1A;

FIGS. 2A–2H illustrate the steps of the prior art “positive crown”method of building a green carcass, entailing the “pre-apexing” methodof affixing an apex onto a bead;

FIGS. 3A–3G illustrate the steps of the prior art “negative crown”method of building a green carcass, entailing the “flat application ofapex” method of affixing the apex onto a bead;

FIGS. 4A–4I illustrate the steps of building a green carcass accordingto the present invention;

FIG. 5A shows a meridional cross-section of a finished radial plypneumatic tire according to the present invention; and

FIG. 5B shows a cross-section of the bead section of FIG. 5A.

DEFINITIONS

“Bead” means an annular tensile member that is associated with holdingthe tire to the rim. The beads are wrapped by ply cords and shaped, withor without other reinforcement elements such as flippers, chippers,apexes or fillers, toe guards and chafers.

“Belt structure” means at least two annular layers or plies of parallelcords, woven or unwoven, underlying the tread, unanchored to the bead,and having both left and right cord angles in the range from 18 to 30degrees relative to the equatorial plane of the tire.

“Meridional” refers to a laterally disposed curved line that lies in aplane that includes the axis of the tire.

“Ply” means a cord-reinforced layer of rubber-coated radially deployedor otherwise parallel cords.

“Radial” and “radially” mean in a direction perpendicular to the axis ofrotation of the tire.

“Radial ply tire” means a belted or circumferentially restrictedpneumatic tire in which at least one ply has cords which extend frombead to bead.

“Sidewall” is the portion of a tire between the tread and the bead.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows a meridional cross-section of a typical conventionalradial ply tire 100, comprising a tread 110, a belt structure (“belts”)112 comprising one or more belts, and a carcass 114. The carcass 114 hasan innerliner 116, at least one radial ply 118, two sidewalls 120A,120B,and two identical bead sections 130A,130B.

FIG. 1B shows a cross-section of the bead section 130A of FIG. 1A. Thereference numbers match those of FIG. 1A. It should be understood thatthe construction of the bead section 130B (not shown) is the same asthat of the bead section 130A. The bead section 130A includes a bead 132comprised of a bundle of wound steel filament in a rubber matrix. Theply 118 is wrapped around the bead, forming a ply inner section 118A anda ply turnup 118B. An apex 134 of rubber is surrounded by the bead 132,the ply inner section 118A and the ply turnup 118B.

In the tire building process, there are two methods of building a greentire carcass (“green” meaning as yet uncured and still tacky), whichdiffer in how the apex is affixed to the bead. The “positive crown”method of building a green carcass includes the “pre-apexing” method ofaffixing the apex. The “negative crown” method of building a greencarcass includes the “flat application of apex” method of affixing theapex.

FIGS. 2A–2H diagrammatically illustrate the steps of the prior art“positive crown” method of building a green carcass, entailing the“pre-apexing” method of affixing an apex onto a bead, showing across-section of a portion of a first stage tire building drum 200 astire components are added and shaped. Although the following descriptionis described in terms of only one side of the tire, it should beunderstood that the procedure applies to the other side of the tire (notshown) as well.

The drum 200 has an axially-central metal surface 242, and an inflatablebladder 244 along the axially-outer portion of its surface. As shown inFIG. 2A, a green rubber innerliner 216 and then a green ply 218(comprised of inextensible polymer cords in a green rubber matrix) areslid over the building drum 200. Then, as shown in FIG. 2B, swab downpaddles 246 swing down (as shown by arrow 252) to press the down theouter portion of the innerliner 216 and the ply 218 and then swing backup (as shown by arrow 253). Then, as shown in FIG. 2C, an apexingmachine (not shown) preassembles (adheres) a triangular green rubberapex 234 over a bead 232 (comprising a cross-sectionally square bundleof wire filaments in a green rubber matrix). Then, as shown in FIG. 2D,the bead 232, with the apex 234 still adhering to it, is spliced to forma ring and is positioned circumferentially around the ply 218. Then, asshown in FIG. 2E, the bladder 244 is inflated to turn up theradially-outer portion of the ply 218, forming a ply turnup 218B whichbends around the bead 232 and the apex 234. Then, as shown in FIG. 2F, agreen sidewall 220 is affixed over (adhered to) the ply 218. Then, asshown in FIG. 2G, the resulting assembly is removed from the buildingdrum 400. The resulting assembly, including the innerliner 216, the ply218, the bead 232 and the apex 234, is called a green carcass 214. Then,as shown in FIG. 2H, the green carcass 214 is inflated to a toroidalshape, and its radially-outer surface is pressed against a tread andbelt package (not shown).

In subsequent steps, the resulting assembly is stitched (rolled with aroller) to remove air pockets and to press internal surfaces together toyield good adhesion between adjacent materials, and the resultingassembly is inserted into a mold to cure under heat and pressure. Duringthe aforementioned shaping process, and especially during curing, whenthe green rubber matrix of the bead 232 temporarily softens, the bead'spreviously square cross-sectional profile becomes semicircular (flat topand round bottom) as it is in the final tire (as shown as bead 132 inFIG. 1B).

The advantages of having the flexibility to design a radially long apexand an apex of multiple layers of different material (“compound apex”)were described in the Background section above. Unfortunately, in thepre-apexing method, described above, the apex must be short and stiff,due to splicing imperfection and the tendency for “curl-over” (both ofwhich are aggravated by increased apex radial length and apex softness).Also, the pre-apexing method is not suitable for making compound apexes,because compound apexes are complex to extrude and prone to deformationwhile standing vertical in the soft green state.

FIGS. 3A–3F diagrammatically illustrate the steps of the prior art“negative crown” (or “flat building”) method of building a greencarcass, entailing the “flat application of apex” method of affixing theapex onto the bead, showing a cross-section of a portion of a firststage tire building drum 300 as tire components are added and shaped.Although the following description is described in terms of only oneside of the tire, it should be understood that the procedure applies tothe other side of the tire (not shown) as well.

The drum 300 has an expandable metal central surface 342 around theaxially-center portion of its surface, and an inflatable bladder 344around the axially-outer portion of its surface. As shown in FIG. 3A, agreen rubber innerliner 316 and then a green ply 318 are wrapped around(over) the building drum 300. A bead 332 (same as bead 232 in FIG. 2B)is positioned around, but not touching, the ply. Then, as shown by thearrows in FIG. 3B, the central surface 342 is expanded radially outwardto tighten against the ply 318, and the axially-inner portion of thebladder 344 is expanded radially outward to tighten against the bead332. Then, as shown in FIG. 3C, an apex 334 (a substantially-triangularstrip of green rubber “gum strip”) is laid over the green ply 318, lying“flat” on its side (from which this apex application method gets itsname), so that one of its tacky sides adheres to the tacky green ply318. Then, as shown in FIG. 3D, the bladder 344 is inflated to turn upthe radially-outer portion of the ply 318, forming a ply turnup 318Bwhich bends around the bead 332 and the apex 334. An undesirable airpocket 354 is formed between the bead 342, the apex 344 and the plyturnup 318B, which is only partially removed by a “stitching” roller.Then, as shown in FIG. 2E, a green sidewall 320 is adhered over the ply318. The resulting assembly, shown in FIG. 3F, including the innerliner316, the ply 318, the bead 332 and the apex 334, is called a greencarcass 314.

The green carcass 314 is removed from the first stage building drum andis mounted on a “second stage machine” (not shown) where it is inflated(reshaped) to a toroidal shape, as shown in FIG. 3G, and itsradially-outer surface is pressed against a tread and belt package (notshown). During this reshaping, the apex 334 swings around 90 degrees torest vertically atop the bead 332. In subsequent steps (as with the“positive crown” method), the resulting assembly is “stitched” (toremove air pockets and adhere adjacent internal surfaces together) andinserted into a mold to cure under heat and pressure to become afinished tire. As in the positive crown method, during the shaping andmolding processes, the bead acquires a semicircular cross-sectionalprofile.

The advantages of having the flexibility to design a compound apex weredescribed in the Background section above. Unfortunately, the “flatapplication of apex” method, described above, is not suitable for makingcompound apexes because increasing the number of apex layers wouldincrease process time and extruder complexity. Also, the “flatapplication of apex” method suffers from entrapped air (originating fromthe air pocket 354 in FIG. 3D) which can cause internal delaminations.

FIGS. 4A–4E diagrammatically illustrate the steps of building a greencarcass according to the present invention, showing a cross-section of aportion of a tire as tire components are added and shaped. Although thefollowing description is described in terms of only one side of the tirecarcass, it should be understood that the procedure applies to the otherside of the tire carcass (not shown) as well.

“Off line” (i.e. before reaching a building drum), as shown in FIG. 4A,an axially-inner apex 434A and an axially-outer apex 434C arepreassembled (applied, adhered) to a ply 418 in the form of thincross-sectionally rectangular “even gum strips” of green rubber lyingflat over the ply. Then, as shown in FIG. 4B, an innerliner 416 and thenthe ply 418 are wrapped around a building drum 400. The drum 400 issimilar to the drum 300 (FIGS. 3A–3F) used in the “negative crown” tirebuilding method. The drum 400 has an expandable axially-central metalsurface 442 and an inflatable bladder 444 along the axially-outerportion of its surface. Then, as shown in FIG. 4C, an apexing machine(not shown) preassembles (adheres) a substantially-cross-sectionallytriangular green rubber middle apex 434B over a bead 432 (comprising across-sectionally square bundle of wire filaments in a green rubbermatrix). Then, as shown in FIG. 4D, the bead 432, with the apex 434still adhering to it, is spliced to form a ring and is positioned around(but not touching) the ply 418 between the inner apex 434A and the outerapex 434C. Then, as shown by the arrows in FIG. 4E, the central surface442 is expanded radially outward to tighten against the innerliner 416and the ply 418, and the axially-inner portion of the bladder 444 isexpanded riadially outward to tighten against the bead 432. Then, asshown in FIG. 4F, the bladder 444 is inflated to turn up theaxially-outer portion of the ply 418, thus bringing the outer apex 434Cup against the middle apex 434B, forming a ply turnup 418B which bendsover the bead 432 and the three apexes 434A–C. Then, as shown in FIG.4G, a green sidewall 420 is adhered over the ply 418. The resultingassembly, shown in FIG. 4H, including innerliner 416, ply 418, bead 432and apexes 434A–C, is called a green carcass 414.

The green carcass 414 is removed from the first stage building drum andis mounted on a “second stage machine” (not shown) where it is inflated(thus reshaped) to a toroidal shape, as shown in FIG. 41, and theradially-outer surface of the carcass 414 is pressed against a tread andbelt package (not shown). This reshaping straightens out the inner apex434A and the outer apex 434C. Apexes 434A–C, adhering together(partially by their own tackiness), comprise a compound apex 434. Insubsequent steps, the resulting assembly is “stitched” (to remove airpockets and adhere adjacent internal surfaces together) and insertedinto a mold to cure under heat and pressure to become a finished tire.

The three apexes 434A–C are of rubber, and can be of the same ordifferent rubber materials. The rubber materials can be either greenrubber (pre-cured), cured thermoset rubber (i.e. does not resoften whenheated), or thermoplastic rubber (i.e. resoftens when heated). Toillustrate the design flexibility of the compound apex of the presentinvention, a compound apex can be comprised of an inner apex ofthermoplastic, a middle apex of green rubber, and an outer apex of curedrubber.

FIG. 5A shows a meridional cross-section of a finished radial plypneumatic tire 500 according to the present invention, comprising atread 510, a belt structure (“belts”) 512 comprising one or more belts,and a carcass 514. The carcass 514 has an innerliner 516, at least oneradial ply 518, two sidewalls 520A,520B, and two identical bead sections530A,530B.

FIG. 5B shows a cross-section of the bead section 530A of FIG. 5A. Itshould be understood that the cross-section of the bead section 530B(not shown) is the same as that of the bead section 530A. The beadsection 530A includes a bead 532. The ply 518 is wrapped around thebead, forming a ply axially-inner section 518A and a ply turnup 518B. Acompound apex 534 is comprised of an axially-inner apex 534A, anaxially-middle apex 534B and an axially-outer apex 534C, and issurrounded by the bead 532, the ply inner section 518A and the plyturnup 518B.

Of the three apexes 534A–C, the inner apex 534A is typicallycross-sectionally the longest and extends radially farthest outward, andthe middle apex 534B is typically cross-sectionally the shortest andextends radially outward the least, although this is not necessary.

Although the compound apex 534 of the present embodiment includes anouter apex 534C, it is within the scope of the present invention for thecompound apex not to include the outer apex but only the inner apex 534Aand the middle apex 534B.

The three materials for the three apexes 434A–C can be chosen to achievecertain tire design characteristics (such as stiffness and handlingcharacteristics), which is not possible with the conventional tirebuilding methods. The compound apex 534 can be very long, because itslongest component (the inner apex 434A) lies on its side while in thegreen state. The greater the flexibility of apex length and the greaterthe flexibility in selecting apex material (both of which are affordedby this invention), the greater the flexibility of, and control over,tire characteristics.

Since the inner apex 434A and the outer apex 434C are laid onto the ply434 off-line (i.e. before mounting the ply 418 on the building drum400), their application does not impede manufacturing throughput.

While the invention has been described in combination with embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the spirit andscope of the appended claims.

1. An unfinished pneumatic radial ply tire assembly comprising: a tread,a belt structure and a carcass; wherein the carcass has a radial ply andtwo bead sections; and wherein the tire is characterized by: each beadsection having a bead and a compound apex comprising an inner apex, amiddle apex and an outer apex; the inner apex and the outer apex have asubstantially rectangular cross-section, and the middle apex has asubstantially triangular cross-section; and the outer apex comprisescured rubber and the middle apex comprises green rubber.
 2. Theunfinished radial ply tire assembly of claim 1 characterized in that:the inner apex extends radially outward further than the outer apex, andthe middle apex extends radially outward less than the outer apex. 3.The unfinished radial ply tire assembly of claim 2 characterized inthat: the inner apex comprises thermoplastic.
 4. A method of building agreen tire carcass comprising the steps of: preassembling an inner apexto a ply; preassembling an outer apex comprising cured rubber to theply; preassembling a middle apex comprising green rubber over a bead;wrapping the ply with the preassembled inner apex around a buildingdrum; splicing the bead with the middle apex to form a ring; and afterwrapping the ply around the drum, positioning the spliced bead aroundthe ply; wherein, when the spliced bead is positioned around the ply, itis positioned between the inner apex and the outer apex.
 5. The methodof claim 4, further comprising: inflating a bladder of the drum to turnup an axially-outer portion of the ply, thus bringing the outer apex upagainst the middle apex, forming a ply turnup which bonds over the beadand the inner, middle and outer apexes.
 6. The method of claim 4,wherein: when the spliced bead is positioned around the ply, it is nottouching the ply.
 7. The method of claim 6, further comprising:inflating a bladder of the drum radially outward to tighten against thebead.
 8. The method of claim 4, wherein: the building drum comprises anexpandable axially-central surface and an inflatable bladder along anaxially-outer portion of its surface.
 9. The method of claim 6, furthercomprising: expanding a central surface of the drum radially outward totighten against the ply.
 10. The method of claim 4, further comprising:adhering a green sidewall over the ply, thereby forming a green carcass.11. The method of claim 10, further comprising: removing the greencarcass from the building drum and mounting it on a second stagemachine, then inflating the green carcass to a toroidal shape andpressing a radially-outer surface of the carcass against a tread andbelt package to form a resulting assembly.
 12. The method of claim 11,further comprising: stitching the resulting assembly and inserting itinto a mold to cure under heat and pressure to become a finished tire.13. The method of claim 4, further comprising: prior to wrapping the plyaround the building drum, preassembling an outer apex to the ply;wherein the inner, middle and outer apexes are of different rubbermaterials.
 14. The method of claim 4, wherein: the inner apex comprisesthermoplastic.
 15. The method of claim 4, wherein: the inner apex has arectangular cross-section.
 16. The method of claim 4, wherein: themiddle apex has a cross-section which is substantially triangular. 17.The method of claim 4, further comprising: prior to wrapping the plyaround the building drum, preassembling an outer apex to the ply;wherein the inner and outer apexes have a rectangular cross-section; andthe middle apex has a cross-section which is substantially triangular.